A number of catalysts containing molybdenum as an active component have been developed, particularly, as catalysts for gas phase catalytic oxidation and are extensively employed in actual production processes. These catalysts are very widely used, for example, in a process of producing acrylonitrile or methacrylonitrile by ammoxidizing propylene or isobutylene, a process for the production of acrolein or methacrolein through the oxidation of propylene or isobutylene, a process for preparing a carboxylic acid such as acrylic acid or methacrylic acid by oxidizing an unsaturated aldehyde such as acrolein or methacrolein or an olefin such as propylene or isobutylene, a process for producing 1,3-butadiene or conjugated diolefin through the oxidation and dehydrogenation of a butene or the like, etc. However, these catalysts exhibit gradual deactivation in the course of use or, in some instances, considerable deactivation in a strongly reducing atmosphere.
In such situations, it has conventionally been a routine practice to maintain the conversion above a predetermined level by replacing a deactivated catalyst with a fresh catalyst. Several methods have been proposed for the regeneration of such a deactivated catalyst. For example, in Japanese Patent Laid-open No. 49201/1975, there is proposed a method for regenerating an oxidizing catalyst by contacting it in a fluidized-bed reactor with fluidized particles consisting of a substantially inert carrier containing molybdenum without interrupting the reaction, considering that one of the paths of the deactivation stems from the loss of molybdenum while the reaction proceeds. In U.S. Pat. No. 4052332, there is proposed a method of regenerating a deactivated catalyst by impregnating same with at least molybdenum and bismuth and then calcining same. East German Pat. No. 137889 proposes a method for regenerating a deactivated catalyst by adding to it one or more components selected from Bi, Cr, Mn, Fe, Co or Ni and then calcining same. However, although the metallic component practically lost from deactivated catalyst is generally molybdenum only, the methods proposed in the above publications require an addition of metallic components other than molybdenum, whereby losing the balance among its components of the optimum catalyst composition, which is adjusted initially and making it difficult to achieve the regeneration effect continually in a repeated fashion. However, it is extremely uneconomical from the practical point of view to charge a fresh catalyst repeatedly.
An object of this invention is to provide a method for regenerating a catalyst which contains molybdenum as an active component and which has been deactivated through use for reaction.